Astronomers using the NASA/ESA/CSA James Webb Space Telescope have spotted a collision of giant asteroids around Beta Pictoris, the second brightest star in the constellation of Pictor.
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Chen et al. show that Beta Pictoris has a dynamic circumstellar environment and that periods of enhanced collisions can create large dust clouds that sweep through the planetary system, increasing the dust accretion onto the giant planets Beta Pictoris b and c. Image credit: Roberto Molar Candanosa / Johns Hopkins University / Lynette Cook / NASA.
Beta Pictoris (β Pictoris) is an A5-type star located about 63 light-years away from Earth in the constellation of Pictor.
The star has a mass of about 1.8 times the Sun and an age of only 20 million years.
It hosts a circumstellar disk of gas and dust; a large number of comet-like bodies; and two giant planets: Beta Pictoris b and c.
Beta Pictoris b is a gas giant approximately 9 to 13 times the mass of Jupiter. It orbits the parent star once every 22 years at a distance of 9.8 AU (astronomical units).
Beta Pictoris c has a mass of 8.2 times that of Jupiter and is much closer to its star. It orbits at 2.7 AU and has an orbital period of roughly 1,200 days.
“Beta Pictoris is at an age when planet formation in the terrestrial planet zone is still ongoing through giant asteroid collisions, so what we could be seeing here is basically how rocky planets and other bodies are forming in real time,” said Dr. Christine Chen, an astronomer at Johns Hopkins University.
Dr. Chen and colleagues spotted significant changes in the energy signatures emitted by dust grains around Beta Pictoris by comparing new data from Webb with observations by NASA’s Spitzer Space Telescope from 2004 and 2005.
With Webb’s detailed measurements, they tracked the dust particles’ composition and size in the exact area previously analyzed by Spitzer.
Focusing on heat emitted by crystalline silicates (minerals commonly found around young stars as well as on Earth and other celestial bodies), they found no traces of the particles previously seen in 2004 and 2005.
“This suggests a cataclysmic collision occurred among asteroids and other objects about 20 years ago, pulverizing the bodies into fine dust particles smaller than pollen or powdered sugar,” Dr. Chen said.
“We think all that dust is what we saw initially in the Spitzer data from 2004 and 2005.”
“With the new Webb data, the best explanation we have is that, in fact, we witnessed the aftermath of an infrequent, cataclysmic event between large asteroid-size bodies, marking a complete change in our understanding of this star system.”
The new data suggests dust that was dispersed outward by radiation from the system’s central star is no longer detectable.
Initially, dust near the star heated up and emitted thermal radiation that Spitzer’s instruments identified.
Now, dust that cooled off as it moved far away from the star no longer emits those thermal features.
When Spitzer collected the earlier data, scientists assumed something like small bodies grinding down would stir and replenish the dust steadily over time.
But Webb’s new observations show the dust disappeared and was not replaced.
“The amount of dust kicked up is about 100,000 times the size of the asteroid that killed the dinosaurs,” Dr. Chen said.
The authors presented their findings this week at the 244th Meeting of the American Astronomical Society in Madison, Wisconsin.
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Christine Chen et al. 2024. The Spectroscopic Case for a Recent Giant Collision Around beta Pic. AAS 224, abstract # 313
